1. Field of Invention
The present invention is related to brake drums, and more particularly brake drums for heavy-duty vehicles having reduced weight without the loss of required braking performance and drum integrity.
2. Background
Like most components for heavy-duty vehicles such as trucks and buses, users desire the lowest amount of weight while obtaining the highest amount of performance. A standard full cast brake drum weight approximately 112 pounds. Unfortunately, prior art brake drums can only be lightened so much before performance suffers, particularly due to heat fatigue caused by braking. Further, to achieve the maximum amount of weight reduction in prior art drums, one must use a premium alloyed iron, thus increasing costs.
Two such examples of prior art attempts to lighten drums but maintain performance are the ArvinMeritor SteelLite X30™ (94 pounds) and the Hayes Lemmerz CentriFuse® (90 pounds). Gray iron is centrifugally cast in a steel shell to provide resistance to heat cracks and breakage problems. However, steel shell drums have brake noise issues and braking heat absorption and dissipation are poor due to the lower volume of gray iron and low heat conduction of the steel shell.
Another prior art attempt is the Gunite Gold drum (94 pounds). High Molybdenum content (>0.6%) and other alloys provide strength at higher braking temperatures. However, dynamometer tests show longer drum life at the expense of a higher tendency of braking fade with much lower deceleration at or above 60 miles per hour.
It is therefore a goal of manufacturers and users of brake drums for heavy duty vehicles to provide a lower drum weight while maximizing the safe and effective operation of the drum. It is further goal to minimize metal fatigue and brake fade based on the temperature of the drum while in use.